FIG. 1 shows a conventional, two-speed dual fan module, generally indicated at 10, for an engine cooling application. The module includes a two-speed motor 12 for operating a first fan, and a one-speed motor 14 for operating a second fan. The typical electrical schematic diagram is shown in FIG. 2, and the truth table for controlling relays 16, 18 and thus the speed of the motors 12, 14 is shown in FIG. 3. Motor 14 achieves two-speed operation by virtue of its connection to the two-speed motor 12. Any low or high-speed combination is possible with this module 10.
FIG. 4 is a sectional view of the conventional two-speed motor 12 of the module 10 of FIG. 1. The motor 12 of FIG. 4 is of the type disclosed in U.S. Pat. Nos. 5,925,999 and 4,910,790, the contents of each of these patents are incorporated by reference into the present specification. This two-speed motor 12 has dual armature windings 20, 22 and dual commutators 24, 26. Any low or high speed combination is possible based on the selection of armature windings.
FIG. 5 is an electrical schematic of a conventional two-speed dual fan module 10′ in a series/parallel configuration having a pair of one-speed motors 13, 15. FIG. 6 shows the truth table for operating relays, K1, K2 and K3 to achieve two speeds for the module 10. Software preferably controls fan speed from OFF to LOW to HIGH speed (reverse order also occurs). LOW speed (SPEED 1) is achieved when both fans (e.g., motors 13, 15 of the module) are operated in series. HIGH speed (SPEED 2) is achieved when both fans (motors 13, 15) are operated in parallel.
Although the modules 10, 10′ operate well for their intended purpose of providing a two-speed dual fan module, there is a need to provide a dual fan module, using existing motors, which can operate at more than two different speeds.